The Case for Cohorts

Higher education already has a proven educational approach we need to consider to help colleges reopen more safely in the fall, writes Peter Plavchan.

June 9, 2020

Imagine it is fall 2020, and your campus has decided to reopen because coronavirus cases in your local region have significantly declined. Alice, an incoming freshman, is signed up for five courses: one in her major of physics and four general education courses. One has a lab of 30 students, another is a recitation section of 30 students and another two are in different large lecture halls with more than 50 students each.

Everyone is wearing masks and washing their hands. Aside from additional precautions for spacing and cleaning, Alice has a typical college semester schedule.

Now imagine Alice meets Bob in her recitation section. A few weeks into the semester, Alice and Bob are both comfortable with one another; they know neither has gotten sick since the start of the semester. Bob has recently contracted COVID-19 through an off-campus job he takes to help pay tuition, but he’s asymptomatic, untested and doesn’t know it. At the time, Bob’s the only coronavirus-positive student on your campus of 30,000 students.

Alice and Bob lower their masks for a few minutes to better hear each other during a think-pair-share exercise while the professor is engaging with other students. As Bob exhales virus particles that disperse through the classroom, Bob unintentionally infects Alice along with several other nearby students from the rest of their recitation section.

Bob is a junior also taking five classes -- three in his major of computer science and two general education classes. However, the recitation section is the only class Alice and Bob attend in common, and taken all together, their combined classes have 500 students. Alice and Bob live in different dorms, too. Over the next two weeks, Alice and Bob accidentally initiate an outbreak that infects hundreds of their fellow classmates in nine different classes and two dorms, as well as staff and faculty members in two different schools within the university. A professor is intubated because Alice met with her one on one in her office during office hours, which was enough for the professor to contract the virus.

Within a month, to stop the outbreak, the campus transitions fully to online instruction. But the damage is done. The campus mourns the death of Charlie, a senior economics student in his last year before graduation, who took all the necessary precautions but had a comorbidity that made him especially vulnerable to the virus.

The Benefits of a Different Model

A recent Cornell University study calculated from academic enrollment alone the size of the network of their average college student before the pandemic. The average student at Cornell, given three degrees of separation, comes into social contact with 98 percent of the student population -- essentially everyone -- through their classes alone. Many other institutions have similar statistics.

In my hypothetical example, all it took was one infected person on the campus to spark an outbreak. Some of our institutions recorded campus community confirmed cases during the spring 2020 semester after we transitioned to online instruction. My own recorded 15 confirmed cases before it stopped publicly reporting them. Any one of these cases could have unleashed an outbreak on our campus that we averted by switching to online instruction.

The draft Centers for Disease Control and Prevention guidelines for reopening, before they were stripped of detailed recommendations, had this recommendation for K-12 education: "Ensure that student and staff groupings are as static as possible by having the same group of children stay with the same staff (all day for young children, and as much as possible for older children). Restrict mixing between groups."

Fortunately, higher education already has the cohort model to look to as a piece in the puzzle for reopening college campuses. That model has a strong and positive academic heritage. Many institutions have implemented the cohort model on a small scale -- for instance, with an honors college or a live-and-learn community. The University of Colorado plans to experiment with this model (in classes only) this fall. The cohort model has been proven to promote retention of students through identity building. Having students take the same classes together and live together leads to overall better academic outcomes, which is especially important during these stressful times of a pandemic crisis.

The cohort model also has real benefits in limiting virus communal spread, by limiting group sizes to a few tens of students. The goal of social distancing is to minimize the number of close social interactions we have to reduce and slow the rate of community spread of COVID-19. A plan to reopen a college campus should maintain similar goals. We want to maximize the number of classes students take in common together in person to minimize the number of distinct physical social interactions each one has. We also want those same students that take classes together to live together, eat together and socialize together.

Widespread adaptation of a cohort model will be a challenge to implement to the maximum extent practical. Students are now free to choose classes independently to suit their schedules, which often involve jobs, caregiving and other outside scheduling constraints. But we know freshman take general education courses, and many have similar courses in common, albeit in different sections or large lectures. In addition, many upper-class students with declared majors take classes in those majors together.

Unfortunately, we are already past the time when students have started registering for classes, and consequently college and universities may be limited to identifying cohorts from students already enrolled in courses together. However, we can shift locations and class times to identify as many cohorts of students as practical to minimize social interactions. Various students’ academic year, declared major, housing choice and so forth are natural boundaries to temporarily put in place to break large social networks and minimize viral campus community spread.

An Alternate Scenario

Now, reimagine that Alice comes to the campus as part of an academic cohort, like an honors college or a live-and-learn community -- an approach deployed to the maximum extent practical across the entire student population. Alice still takes five courses, but this time all of her classes have roughly the same 20 students, and she takes them in the same physical classroom. Some of her instructors teach her in person in their cohort’s dedicated classroom; others in at-risk groups teach her virtually.

Alice still meets her major and general education requirements. Her cohort shares her major of interest and class year. They live in the same dorm and socialize with one another. They form durable social bonds that help their retention. They work on assignments together. The start and end times of their classes are staggered as much as possible, so when they walk between their dorm, cafeteria and classroom, they walk as a group and encounter few others. They still wear masks, and the campus still cleans and sanitizes regularly. Once a week, someone from their cohort is randomly tested for COVID-19, aiding contact tracing and mitigation. Most important, Alice never comes into physical contact with Bob.

Bob is also in a cohort in engineering with 40 other junior computer science majors; they also share a dorm floor. It’s the biggest cohort size on campus. Most of his classes are major courses, all taken with the same 40 students, while they take one of two electives with about 20 students each, and a large general education course virtually. Bob does infect half of the students in his cohort, but that is the extent of the campus outbreak. University administrators discover it after two weeks when they randomly test one of the 20 infected students in his cohort or another student reports symptoms. All 40 students self-isolate -- courses for that particular cohort are suspended or taught virtually -- and do not return from quarantine until after they’re all tested. Additional testing is conducted for other cohorts.

The professor who meets with Alice also avoids catching COVID-19. As for Charlie, he never comes into social contact with those 20 infected students in engineering; he’s part of a cohort of his own in economics that’s opted for all virtual instruction, and he lives to graduate. And the university averts an outbreak and doesn’t need to transition to all virtual instruction.

Which scenario would you choose?


Peter Plavchan is assistant professor of physics and astronomy at George Mason University.


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